Polyamide resins have been the subject of much research since the 1930s. This research has been directed toward improving the processability of polyamide resins.
It is known in the art to copolymerize polyamide forming species and dimer acids or dimer diamines. The trend in the past has been to polymerize substantial amounts of dimer acids with other polyamide-forming species to improve mechanical and rheological properties. See, for example U.S. Pat. No. 4,062,820 and British Pat. No. 1,319,807. In U.S. Pat. No. 3,549,573 there is disclosed such a polymerization employing a dimer acid, a short chain dibasic organic acid and a short chain organic diamine. Undesirable characteristics of the aforementioned adhesives often included insufficient impact resistance or unsuitability as hot melt adhesives due to excessive melt viscosity. Where polyamides having a limited amount of dimer acids were prepared as low melt viscosity resins they exhibited low impact strength and were excessively crystalline and brittle. See, for example, U.S. Pat. No. 4,018,731.
In U.S. Pat. No. 4,128,525 and related U.S. Pat. Nos. 4,162,931 and 4,182,845, all to Yeakey, there is disclosed a method for preparing thermoplastic adhesives having a broad range of hardness, flexibility and compatibility from synthetic materials comprising polyoxypropylene polyamines, short-chain aliphatic or aromatic dicarboxylic acids, esters or anhydride and piperazine. Here, attention is drawn to the fact that, although vegetable and animal based long-chain dimer or trimer fatty acid materials are conventionally employed in the preparation of polyamide-based thermoplastic adhesives, such sources are not as plentiful as they once were due to increased market demands. Thus, adhesives made using synthetic components would be desirable.
U.S. Pat. No. 4,218,351 describes a copolyamide which is the product of a short chain polyamide-forming species, a polyamide-forming dimer acid and amorphous polyamide forming oligomers having an average molecular weight in the range of 600 to 10,000. These polyamides are tough, flexible and impact resistant and are well suited for use as hot melt adhesives.
In Ger. Offen. 2,814,566 there is disclosed a process for preparing hot-melt adhesives from piperazines and compounds of the formula: EQU H.sub.2 NCHMeCH.sub.2 (OCHRCH.sub.2).sub.n OCH.sub.2 CHMeNH.sub.2
where R=H or Me and having a molecular weight of 200-800 and a mixture of C.sub.2-7 alkanedioic acid and a C.sub.8-14 alkanedioic acid.
In a publication titled "Polyamides From JEFFAMINE.RTM. Poly(Oxypropylene)Amines-Preparation And Use In Hot Melt Adhesives", Texaco Chemical Co.(1975), there is disclosed the use of polyoxyalkylene diamines such as those sold by Texaco Chemical Co. as JEFFAMINE.RTM. D-series products in the synthesis of thermoplastic polyamides to form intermediates. The intermediates are then reacted with standard bisphenol A-based epoxy resins to produce adducts which are useful as hot melt adhesives. It was reported the adhesives so produced performed well in bonding aluminum to aluminum and steel to steel, as well as bonding canvas and vinyl to various substrates.
It would be a substantial advance in the art if hot melt adhesives could be produced which exhibited improvements in properties such as elasticity and tact, as well as exhibiting a wide range of softening points and tensile shear strengths which can be obtained in a predictable fashion by adjusting the ratio of components.